This invention relates in general to temperature monitoring devices and deals more particularly with an improved device for monitoring operation of a steam trap. In a steam generating system it is usual to provide a steam trap which removes condensate from the system without appreciable loss of steam. Steam traps conventionally employ a float or other element responsive to the accumulation of liquid condensate for periodically opening a condensate outlet valve to discharge liquid condensate. Condensate is normally removed from the trap through a condensate line connected to the trap and may be returned to the steam generator through return lines for regeneration. When the steam trap malfunctions, steam escapes with condensate through the condensate line which results in heat loss and reduction in the efficiency of the system. Such malfunction is difficult to detect, particularly in a closed system such as aforedescribed where steam leaks through the trap and into the condensate return lines. Heretofore, various means have been provided for detecting when a steam trap is malfunctioning or "leaking through." Such devices have included transparent piping at the steam trap outlet to facilitate visual inspection. However, such clear piping usually becomes coated with rust or other residue from the system within a relatively short time and is wholly ineffective as a leak detector unless cleaned frequently. Bleed valves have also been provided on the condensate lines in such systems. However, such valves must be manually opened and inspected for escaping steam. Unless such inspections are frequent, trap malfunction may go undetected for a long period. Another system, illustrated and described in U.S. Pat. No. 3,926,368, utilizes a thermosensitive indicator strip which is taped or otherwise secured to the condensate line on a trap and which changes color to provide indication of steam within the condensate line. Trap malfunction results in the destruction of the indicator strip which must be replaced if its monitoring function is to be maintained. Such an indicator strip provides an inactive or passive indication of malfunction. A malfunction may go undetected unless the strip is closely scrutinized. Further, where such a steam trap monitoring device is used, it must be assumed that in the absence of indication of malfunction the steam trap and the related portions of the system are functioning properly, because the device does not provide positive indication of proper operation.
It is the general aim of the present invention to provide an improved steam trap monitor which operates substantially continuously to indicate either proper function or malfunction. It is the further aim of the invention to provide an improved substantially self-contained unit which will operate for a long period without maintenance and which may be manufactured at low cost and installed by a person of ordinary skill.